In the field of silver halide photographic elements, it is a common practice to incorporate into a layer of the photographic element appropriate dyes absorbing specific wavelengths of light. Said dyes may be used in any layer of the photographic element, such as an interlayer, a radiation sensitive layer, an overcoat layer, an undercoat layer, a backing layer, and may be used for a variety of purposes, such as filter dyes, antihalation dyes, antiiradiation dyes or for the sensitivity control of the photographic emulsion.
The layers of the photographic elements to be added with the dyes are usually made of gelatin or other hydrophilic colloids. The dyes should have an appropriate spectral absorption according to the intended use, should be photographically inert (not affording adverse effects--such as a decrease of sensitivity, fading of the latent image, and fogging--on the performance of the silver halide emulsion layer), should be colorless, decolored or dissolved and removed during the photographic processing, and should leave little or no stain in the processed film.
Recently, information recording equipment using semiconductor laser diodes emitting in the infrared region of the electromagnetic spectrum have been developed which require silver halide photographic elements sensitive in the same area. Examples of such equipment are the laser scanners using laser diodes which have a much longer operational life and are less expensive and smaller than conventional gas lasers such as helium-neon or argon lasers. The infrared sensitive silver halide photographic elements for use with laser scanners using laser diodes need dyes for halation prevention and irradiation prevention. These dyes must absorb light in the infrared region. To this purpose, many infrared absorbing dyes have been hitherto proposed. U.S. Pat. No. 4,362,800 discloses indolotricarbocyanine dyes having two sulfoalkyl groups for use in antihalation layers, which, however, leave a greenish stain after processing. To solve the problem of staining, indolotricarbocyanine dyes for use as infrared absorbing dyes have been proposed in U.S. Pat. Nos. 4,839,265; 4,871,656; 4,876,181 and 4,933,269 and in European Patent Application Nos. 342,576 and 342,939.
A problem with these dyes is their inability to have adequate spectral absorption in the infrared region of the electromagnetic spectrum. Usually said dyes have an absorbance maximum in the desired wavelength range in molecular form but aggregate to cause a shift in the maximum absorbance wavelength. Accordingly, a deaggregating compound is usually necessary to enable said dyes to have the desired absorption maximum wavelength. Deaggregants, however, can cause adverse photographic effects, such as speed loss during storage. U.S. Pat. No. 4,871,656 discloses certain indolotricarbocyanine infrared filter dyes which do not require a deaggregant, because said dyes have an absorbance maximum in the desired wavelength range in the molecular form and do not aggregate. In particular, dyes having molecular absorption at wavelengths that are not too short are preferably benz[e]indoletricarbocyanine dyes. However, benz[e]indole rings are prepared from dangerous naphthylamine starting compounds. Accordingly, there is still the need to provide infrared absorbing filter dyes having their molecular absorption in the desired wavelength range, without a shift to the desired wavelength range brought about by aggregation, and which dyes can be synthetized using non-toxic intermediates.
U.S. Pat. No. 4,933,269 describes indolotricarbocyanine infrared absorbing filter dyes, having a 5- or 6-membered heterocyclic ring attached to the methine chain. Examples of heterocyclic rings include piperidine, pyrrolidine, indoline, 3-pyrroline, piperazine, morpholine, thiomorpholine, and other saturated heterocyclic rings. However, it has been noted in the present invention that the filter dyes of U.S. Pat. No. 4,933,269 display radiation absorption at wavelengths at or beyond 750 nm, when they are benz[e]indolotricarbocyanine dyes and aggregate.
Another problem with indolotricarbocyanine infrared absorbing filter dyes is that they have relatively narrow spectral absorption curves. Accordingly, such dyes may have problems when used with laser diodes emitting at different wavelengths of the infrared region (typical laser diode emission wavelengths are about 750, 780, 800, 820 and 870 nm) or when used with commercial samples of the same laser diode which frequently have variations in the wavelength of the emitted infrared light.
French Patent No. 1,544,726 describes tricarbocyanine dyes, for use as filter or spectral sensitizing dyes, having the formula: ##STR2## wherein n represents an integer of 1 or 2, R represents an alkyl or an aryl group, R.sub.1 and R.sub.2 each represents an alkyl, an alkoxycarbonylalkyl or an aryl group, R.sub.3 and R.sub.4 each represents an hydrogen atom, a halogen atom, an alkyl or an alkoxy group, X represents an anion, m represents an integer of 1 or 2, provided that m is 1 when R represents a carboxyalkyl or a sulfoalkyl group, and Z represents the atoms necessary to complete a thiazole, benzothiazole, naphthothiazole, thionaphtheno-7',6',4,5-thiazole, oxazole, benzoxazole, naphthoxazole, selenazole, benzoselenazole, naphthoselenazole, thiazoline, 2-pyridine, 4-pyridine, 2-quinoline, 4-quinoline, 1-isoquinoline, 3-isoquinoline, 3,3-dialkylindolenine, imidazole, benzimidazole or naphthimidazole. Said dyes are said to have a maximum absorption in organic solvents between 750 and 800 nm and aggregate when in water solution to give maximum absorption in the range of 950 to 1090 nm. In said patent there are specific examples of tricarbocyanine dyes derived from benzoxazole or benzothiazole nucleus in which R.sub.1 may be a methyl group and R.sub.2 may be a phenyl group.
Despite of the fact that by selecting among many substituents there is the possibility of having R.sub.1 different from R.sub.2 in tricarbocyanine dyes (see U.S. Pat. No. 4,871,656, EP 251,282 and FR 1,544,726), no one of said references has specifically recognized that when R.sub.1 is different from R.sub.2 in tricarbocyanine dyes derived from indole nucleus, dyes are provided which have spectral absorption in the infrared region without aggregating in water and relatively broad spectral absorption curves.